Electrical contact for high voltage power circuit current

ABSTRACT

In a high voltage, gas-filled power circuit current interruption apparatus, an improved electrical contact comprising a conductive base member, a conductive mounting member disposed in and electrically coupled to the base member, and a conductive electrode, disposed in the mounting member. The mounting member supports the electrode on the contact and is constructed of an electrically conductive composition which has a coefficient of thermal expansion similar to that of the electrode. Thermal stress resulting from heating of the electrode and mounting member by current arcs remains approximately constant over a specified temperature range, and damage caused thereby is prevented.

United States Patent 1191 Rolff et al..

[ 1 ELECTRICAL CONTACT FOR HIGH VOLTAGE POWER CIRCUIT CURRENT [75] Inventors: Klaus-Peter Rolif; Peter Huhse, both of Berlin, Germany [73] Assignee: Siemens Aktienge'sellschaft, Munich Germany 221 Filed: Mann, 1973 2: Appl. No.: 344,045

[30] Foreign Application Priority Data 14 1 Apr.-2, 1974 Attorney, Agent, or Firm-Kenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT In a highv voltage, gas-filled power circuit current interruption apparatus, an improved electrical contact comprising a conductive base member, a conductive mounting member disposed in and electrically coupled to the base member, and a conductive electrode, disposed in the mounting member. The mounting member supports the electrode on the contact and is constructed of an electrically conductive composition which has a coefficient of thermal expansion similar to that of the electrode. Thermal stress resulting from heating of the electrode and mounting member by current arcs remains approximately constant over a specified temperature range, and damage caused thereby is prevented.

9 Claims, 2 Drawing Figures ELECTRICAL CONTACT FOR HIGH VOLTAGE POWER CIRCUIT. CURRENT BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to electrical power circuit interrupters, and, in particular, to a dielectric gas-filled, high voltage power circuit current interrupter apparatus utilizing improved electrical contacts which are resistant to fractures andother damage caused by thermal stress produced by. arcing currents during interruption of the current flow through the apparatus.

2. Description of the Prior Art Gas-filled electric circuit breakers which utilize a dielectric gas as an arc extinguishing and insulating medium are known. Such a circuit breaker is disclosed in German patent 1,154,548, which teaches the use of an electronegative, flourine-containing gas to fill the circuit breaker. Generally speaking, such circuit breakers include bridge contacts which are movable with respect to the electrical contacts of the devicefor conducting and interrupting the current flowbetween the contacts, and the electrical contacts thereof have generally been constructed of carbon material, such as graphite, in order to reduce bothdamage to the contacts and prevent the production of'decomposition products during current arcing between the electrical contacts when the current flow is interrupted. The graphite contacts used are generally solid members which are slideably disposed in cup-shaped electrodes, and are usually formed in two portions with the outer diameter of one portion being greaterrthan the outer diameter of the other so that the larger portion overlaps the edge of the electrode, and provides a secure mechanical and electrical connection therebetween. German patent 1,488,904 also discloses a switchingdeviceutilizinggraphite electrodes.

In such electric circuit'breakers and switches, however, excessive heating and burning of'the electrodes takes place during current interruption by current arcs flowingbetween the contacts and bridge, which heating tends to break downtheelectrodes of the, circuit breaker and cause the, contacts to fracture, the latter being caused .by expansion of the excessively heated electrode against the cooler contact. Destruction of the contacts and electrodes of the circuit breaker by the constant interruption of the current flow therethrough thus results.

SUMMARY OF THE INVENTION.

contact is provided for a high voltage power circuit current interrupter apparatus, which is filled with a dielectric gaseous insulatingand arc extinguishing medium.

and includes at least one electrically conductive, movable bridge coupling the'electrical contacts conducting current through the apparatus. The improvedcontact comprises an electrically conductive base member having an opening in one end thereof, in which an electri- 2- cally conductive mounting member, having openings in itsends, is slideably disposed. An electrically conductive electrode is disposed in one end 'of the mounting member. The mounting member conducts the current flowing between the bridge of the apparatus and the electrical contacts, including arc currents which flow during interruption of the electrical power, and the material of which it is constructed is chosen to have a coefficient of expansion whose characteristics are similar to that of the electrode, which causes the mounting member to expand during current arcing with the electrode disposed therein so that expansion of the electrode is not restricted by the mounting member, and the thermal stress exerted on the electrode remains constant despite the excessive heating of the electrode. An improved electrical contact which is resistant to damage and fracture caused by current arcing during interruption of electrical power, and yet still provides a secure friction connection between the electrode and contact, is thus achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view of a high voltage, gas-filled, power circuit current interruption apparatus including improved electrical contacts constructed according to the invention;

FIG. 2 is an exploded, partial sectional view of'the composite structural elements comprising an improved electrical contact constructed according to the'inven tion.

In the drawings, similar reference numerals denote similar elements throughout the several views.

DETAILED DESCRIPTION According to the invention, the improved electrical contact comprises a hollow conductive'base member, in which a hollow conductive mounting member is slideably disposed for supporting a hollow conductive electrode on .the end of the base member. The electrode has a known coefficient of thermal expansion and includes a tapered longitudinal bore which forms a nozzle and vents gases generated by current arcing from the current interrupter apparatus. The mounting member is constructed of an electrically conductive metallic composition having a coefficient of expansion which has characteristics similar to that of the electrode. Specifically, if the electrode is constructed of graphite, the mounting member may, for example, be constructed of a metallic composition consisting of about 36 percent nickel and about 64 percent iron, an iron alloy known as Invar. This combination produces favorable material matching, and as a result, the thermal stress exerted on the electrode by the mounting member, i.e., that stress acting on the electrode caused by prevention of its expansion by the mounting member, remains constant over a temperature range of up to about 200C. The annular mounting may also be constructed of an electrically conductive metallic composition consisting of about 28 percent nickel, about 18 percent cobalt, and

about 54percent iron. A favorable material match is also obtained with this composition, since the forces exerted on the electrode by the mounting member reing member. By utilizing the above described improved electrical contact, which reduces the effects of thermal stress on the electrode thereof, destruction of the contacts of the circuit interrupter is significantly reduced, and reliability of the interrupter apparatus is significantly increased.

It is to be understood that the embodiment of the invention illustrated in the accompanying drawings and described herein in the detailed description is an illustrative example only, and it is not intended that the drawings and description comprise a definition of the limits and scope of the invention disclosed therein.

Referring now to the drawings, specifically FIG. 1, there is shown a high voltage, gas-filled power circuit current interrupter which includes a housing 10, constructed ofdielectric material, such as, for example, porcelain. A dielectric gaseous medium, such as, for example,'sulfur hexafluoride, is disposed in the interior space'12 of housing 10. A pair of oppositely disposed electrical contacts are disposed within housing 10, and include hollow, electrically conductive base members 1 having openings in the endsthereof. At least one electrically conductive bridge 11 disposed longitudinally in housing adjacent base members 1 engages the base members. Bridge 11 spans the gap therebetween and conducts current flowing between the contacts in the circuit interrupter. On the right side of FIG. 1, bridge 11 is shown in its electrically conductive position; on the left side of FIG. l, bridge 11 is shown in its current interruption position. It should be noted that alternative positions of a pair of bridges for the circuit interrupter have been illustrated in FIG. 1, and that during operation of such a current interrupter having a pair of conductive bridges both would be disposed in corresponding positions on each side of the electrical contacts. An electrically conductive, hollow annular mounting member 4 is slideably disposed within each 1 of base members 1, and supports an electrically conductive electrode 6 which may, for example, be constructed of graphite. The electrode includes a tapered longitudinal bore which forms a nozzle for venting gases generated during current arcing between base members 1 from interior space 12 'of housing 10.

FIG. 2 illustrates base member 1, mounting member 4', and-electrode'6 of the circuit interrupter in detail. Base memberl is a tubular cylinder, and is provided at its end face 2 with a longitudinal, internal thread 3. Annular mounting member 4 includes upper and lower portions having "different diameters, the lower portion having a smaller diameter than the upper portion thereof and including external threads on the outside surface thereof which are slideably received by internal thread 3 of the base member 1. Electrode 6 is slideably disposed in, and frictionally engaged by, mounting member 4, and is thereby secured on the base member. Electrode 6 is also provided with upper and lower portions having different diameters. Upper portion 7 has a diameter which is slightly greater than the inside diameter of mounting member 5; specifically, outside diameter D of electrode 6' is about 0.1 to about 0.5 percent greater than the inside diameter d of the mounting achieved.

If this steel is used, the thickness of the walls of annular member 4 are made relatively thin so that the member is elastic and thermal stresses generated by current areing, which cause different thermal expansions of the electrode, are elastically absorbedby annular mounting member 4. Alternatively, the metallic composition may comprise 36 percent nickel and 64 percent iron. This composition is able to withstand frictional forces generated by thermal stress acting on the electrode over a temperature range up to approximately 200C. Above that temperature, the thermal stress forces produced become significantly less. For much higher thermal stresses, particularly for temperatures which range above 400C, a conductive composition comprising 28 percent nickel, 18 percent cobalt and 54 percent iron is preferable. Such a metallic composition characteristically expands with increases in temperature up to approximately 400C, in a manner which for the most part corresponds to the expansion of the graphite electrodes over the same temperature range. Mounting of a graphite electrode on the base member of the contact by means of such a mounting member, consisting of one of the foregoing compositions, ensures both good electrical and mechanical coupling of the electrode to the base member, while at the same time assuring that excessive thermal stress is not applied to the graphite electrode by the mounting member securing it to the base member. A mounting structure for mounting a graphite electrode on an electrical contact,-which is damage resistant over a wide range of temperatures, is thereby provided. 0

During interruption of the current flow through the current interruption apparatus, the electrical contact functions as follows; I v

The dielectric gas disposed in interior space 12 of housing 10 is suppliedthereto from a pressurized source (not shown) at a specific pressure, preferably 16 kg/cm The gas serves both'as a quenching medium for extinguishing current arcs'flowing between the base members and as an insulator. When bridge 11 is moved to its non-conductive'position, as the electrical power flowing through the circuit interrupter is interrupted, a current are flows from base member 1 to bridge 11. The mounting member conducts the current flowing through the circuit interrupter, and also conducts any the' are burning from the mounting member to the bridge is rapidly extinguished. Thermal stresses produced by current arcing, which in conventional electrical contacts are caused by the electrodes thereof expanding against the base member, which cause damage to the contact in theform of fractures thereof, are thus eliminated. Furthermore, the gases generated by current arcs, which reduce the quenching efficiency of the gaseous medium in space 12, are also eliminated by the venting of the gases from housing 10. More efficient and highly reliable operation of the interrupter is thus While there has been disclosed herein a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made thereunto without departing from the invention, and it is therefore intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a high voltage power circuit current interruption apparatus, of the type filled with a gaseous dielectric medium and including at least one movable electrically conductive bridge coupling the electrical contacts conducting current through the apparatus, an improved electrical contact, comprising a base member having an opening in at least one end thereof;

a mounting member, including an opening in at least one end thereof, disposed in one end of said base member; and

an electrode, slidably disposed in and frictionally engaging the other end of said mounting member.

2. The electrical contact as recited in claim 1, wherein said electrode, mounting member and base member are hollow and have openings in the ends thereof and vent from the apparatus gases generated by current arcing during interruption of the current conducted between the contacts by the conductive bridge.

3. The electrical contact as recited in claim 2, wherein saidelectrode, mounting member and base member are annular in shape, and wherein saidelectrode includes a tapered longitudinal bore which forms a nozzle therein.

4. The electrical contact as recited in claim 1, wherein said mounting member and said electrode are constructed .of conductive compositions each having similar coefficients of thermal expansion, whereby thermal stress applied to said electrode by said mounting member in response to heating by current arcing remains approximately constant over a specified temperature range.

5. The electrical contact as recited in claim 4, wherein said mounting member is constructed of an electrically conductive metallic composition consisting of about 36 percent nickel and about 64 percent iron, and wherein said electrode is constructed of graphite.

6. The electrical contact as recited in claim 4, wherein said mounting member is constructed of an electrically conductive metallic composition consisting of about 28 percent nickel, about 18 percent cobalt and about 54 percent iron, and wherein said electrode is constructed of graphite.

7. The electrical contact as recited in claim 4, wherein said electrode includes upper and lower portions of different diameters, the outside diameter of the upper portion of said electrode being about 0.1 to about 0.5 percent greater than the inside diameter of said mounting member and the outside diameter of the lower portion of said electrode at room temperature, said lower portion of said electrode being disposed in said mounting member for mounting said electrode therein.

8. The electrical contact as recited in claim 1, wherein said mounting member comprises a thin elastic annular wall of metallic material, expansion of said electrode against said mounting member in response to heating by current arcing being elastically absorbed by said mounting member wall.

9. The electrical contact as recited in claim 8, wherein said mounting member is constructed of an electrically conductive metallic composition consisting of steel type ST 35, and wherein said electrode is constructed of graphite.

TTATES ERQEENT ()FFL L'QE eomeoiiom Patent No. D t dAPTil 2, 1 9%!- Invenfiofls) eKlaue- -Peter'Rolff, Peter Huhse It eert ified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In fine Foreign Replication Priority Data change the file bomber of the German application upon which the olaim for priority'i's based from 2215883" to 49 22 15 883.

Signed and sealed this low day of Se tember 1974.

(SEAL) Aties't: I

MCCOY M. GIBSO1\T JR. c. MARsmLL mm flit-testing Officer Commissioner of Patents FQM PC4050 I I USCOMM-DC eoa1e ce US. GOVERNMENT PRINTING OFFICE: 1969 0-366-334,

UNITED "swam OFFEQE @ERTEFEQATE QGRREQTIQN Fatent No. 3,8013% D April 2, 197

Inventor(s) .Klaus Pster Rolff, Peter Huhse It certified that error appears in the above-identified patent g and that said Letters Patent are hereby corrected as shown below:

In the Foreign fitplioation Priority Data change the file humber of the German application upon which the elaim for priority is based from "2215883" to --P 22 15 883A Signed arid sealed this 3. th day of September 197 (SEAL) ttest:

MCCOY M. GIBSON, JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents $69) USCOMM-DC 60376-P69 .5. GOVERNMENT PRINTING OFFICE; [969 03$5"33" 

1. In a high voltage power circuit current interruption apparatus, of the type filled with a gaseous dielectric medium and including at least one movable electrically conductive bridge coupling the electrical contacts conducting current through the apparatus, an improved electrical contact, comprising a base member having an opening in at least one end thereof; a mounting member, including an opening in at least one end thereof, disposed in one end of said base member; and an electrode, slidably disposed in and frictionally engaging the other end of said mounting member.
 2. The electrical contact as recited in claim 1, wherein said electrode, mounting member and base member are hollow and have openings in the ends thereof and vent from the apparatus gases generated by current arcIng during interruption of the current conducted between the contacts by the conductive bridge.
 3. The electrical contact as recited in claim 2, wherein said electrode, mounting member and base member are annular in shape, and wherein said electrode includes a tapered longitudinal bore which forms a nozzle therein.
 4. The electrical contact as recited in claim 1, wherein said mounting member and said electrode are constructed of conductive compositions each having similar coefficients of thermal expansion, whereby thermal stress applied to said electrode by said mounting member in response to heating by current arcing remains approximately constant over a specified temperature range.
 5. The electrical contact as recited in claim 4, wherein said mounting member is constructed of an electrically conductive metallic composition consisting of about 36 percent nickel and about 64 percent iron, and wherein said electrode is constructed of graphite.
 6. The electrical contact as recited in claim 4, wherein said mounting member is constructed of an electrically conductive metallic composition consisting of about 28 percent nickel, about 18 percent cobalt and about 54 percent iron, and wherein said electrode is constructed of graphite.
 7. The electrical contact as recited in claim 4, wherein said electrode includes upper and lower portions of different diameters, the outside diameter of the upper portion of said electrode being about 0.1 to about 0.5 percent greater than the inside diameter of said mounting member and the outside diameter of the lower portion of said electrode at room temperature, said lower portion of said electrode being disposed in said mounting member for mounting said electrode therein.
 8. The electrical contact as recited in claim 1, wherein said mounting member comprises a thin elastic annular wall of metallic material, expansion of said electrode against said mounting member in response to heating by current arcing being elastically absorbed by said mounting member wall.
 9. The electrical contact as recited in claim 8, wherein said mounting member is constructed of an electrically conductive metallic composition consisting of steel type ST 35, and wherein said electrode is constructed of graphite. 